1. Field of the Invention
This invention relates to surface controlled subsurface safety valves. More particularly, it relates to a well safety valve, connectable in a well tubing string for controlling fluid flow therethrough, in which the valve closure means is operated by a longitudinally movable, telescoping tubular member which is automatically resettable and which has a pressure equalizing feature.
2. Prior Art
The flow of fluids through well tubing is usually controlled by a safety valve placed in the well tubing. The safety valve can be placed in the tubing string itself, and is retrievable with the tubing string. The safety valve closure means may be of the ball, poppet or flapper type. These are generally operable by the longitudinal movement of an operator tube, such as illustrated in U.S. Pat. No. 3,273,588, issued to W. W. Dollison.
Generally, surface controlled subsurface safety valves are operated by conducting control fluid, under pressure, from the well surface to the subsurface valve. The control fluid acts upon the operator tube, which in turn operates the well safety closure means. In the event there is excessive force applied to the operator tube there is a possibility that the safety closure member may be damaged. This is particularly troublesome with flapper type closure members.
U.S. Pat. No. 3,981,358 illustrates one attempt at solving this problem. In that patent there is provided a well safety valve for controlling fluid flow through a well tubing in which the longitudinally movable operator tube included telescoping sections which reduced damage to the valve member. Once telescoped, however, it was necessary to run a tool in the well to reset the telescoping operator tube, or for locking open the valve closure member in the open position. This was time consuming and very expensive.
An effort was made to eliminate the resetting trip down the well tubing by provision in U.S. Pat. No. 4,077,473, of an automatic reset mechanism. This valve utilizes a single control conduit and one main spring for opening and closing the valve closure member. The telescoping sections use a ratchet mechanism to maintain the relative positions of the operator tube sections. Upon excessive resistance to downward control pressure, the ratchet coupling of the tubular section gives way and the sections collapse. Means are provided to hold the lower section in place while the main spring re-extends the collapsed operator sections, upon release of control pressure.
The main disadvantage of this is that the spring must overcome the hydrostatic head of fluid in the control line plus the force of the collect fingers of the "ratchet" mechanism. This severely limits the effective depth at which such valve could be used.